The instant invention relates to a compression bar such as is used in the main drafting zone of drafting rollers in the textile industry.
The drafting rollers constitute the core of a draw frame. Textile fiber slivers are presented to the drafting rollers and drafting of the fiber slivers takes place therein. As it is drawn through the drafting zones, the fiber sliver is spread out into a fiber fleece and is again formed into a fiber sliver after leaving the last drafting zone. The extent of drafting must be adapted to the fiber sliver material, with the staple length being an important material parameter. The drafting equipment consists of a number of roller pairs placed one behind the other and creating drafting zones. Normal drafting rollers generally create a pre-drafting zone and a main drafting zone. To be able to draft textile fiber slivers with fibers of different staple lengths with the same drafting rollers, the distance between the nips of roller pairs can be adjusted. As the distances between nips is increased, special guidance is required in the main drafting field, at least for shorter fibers. This is done by means of the compression bar. The compression bar is a non-moving, fixed bar extending over the width of the drafting rollers. The compression rod deflects the fiber fleece away from its direction of movement.
In a known embodiment, the compression rod has a circular cross-section (Johannsen, O.; Handbuch der Baumwollspinnerei, vol. II, 5th edition, Bernh. Friedr. Voigt Verlag Handwerk und Technik, Berlin-Hamburg, page 120 (II), Fig. F15) or a semi-circular cross-section (VSM prospectus of the Vouk company at ITMA 1991). Also known is a compression bar with a rectangular cross-section, the face of which is in contact with the fiber fleece being rounded and the face away from the fiber fleece being formed by a plane surface sloped towards the longitudinal axis (Operating Instructions, draw frame: RSB 851 (4135), SB 851 (4135) of RIETER Spinning Systems of August 1990, page 24, 4.4.2.4, page 25, Fig. 4, page 26, Fig. 5).
Compression bars with a circular cross-section are also known. They have however the disadvantage that deposited fibers form laps on the compression bar which could disturb the fleece.
It has been shown that many deposits occur with the profiles of conventional compression bars. The deposits are fibers, dust and dirt particles, and finish. Since the compression bar touches the running fiber fleece and deflects it, the fiber fleece is compressed at the point of deflection. As a result deposits from the fiber fleece are deposited on the compression bar. If these deposits become compressed they fall on the fiber fleece and produce a jolt as they pass the exit roller pair, risking to influence the rotational speed ratio of the roller pairs to their detriment. It is however especially disadvantageous that these deposits are conveyed as far as into the sliver funnel and restrict or clog its cross-section. Fiber sliver transportation is affected and sliver quality is impaired.
The dropping of deposits from the compression bar unto the fiber fleece is intensified if the pneumatic aspiration is too weak or is disturbed on the drafting rollers.
As described below, the fiber fleece is also subjected to disadvantageous influence. A delimitation is formed on the compression bar between dirt deposit and dirt-free zone. After switching over to a batch with rougher fiber material, the dirt layer exerts a brake effect upon the surface of the fiber fleece. Surface drafting disturbances may occur.